There is known a turbo-molecular pump having a rotor that rotates at high speeds in a casing with a means that prevents energy generated by breakage of the rotor from being transmitted to the casing outside the rotor (cf., for example, Patent Reference 1). The one disclosed in Patent Reference 1 is provided with double inner casings inside the outer casing.
Patent Reference 1: Japanese Patent Laid-open Publication No. 2001-82379 (especially FIG. 2)